Method of laminating a plastic film having transverse corrugations

ABSTRACT

A method of producing corrugated sheets of thermoplastic material by supplying a softened film over an embossing roller to form first, second and third sets of parallel corrugations which radiate from a common center to define a plurality of star shaped cells and sandwiching the corrugated film between outer films to define pockets.

This invention relates to a sheet material and in particular relates toa plastics sheet material suitable for use in the packaging industry.

In many ways plastics material is ideally suited for the manufacture ofpackages, e.g. cartons and the like, especially for the transport offoods such as fruit, vegetables and meat. Plastics materials aregenerally inert and do not absorb water or any other liquors which maybe exuded by the product carried. So-called corrugated plastics materialboards are particularly useful in this regard since they combine lightweight with relatively rigidity. However, even these boards have thedrawback that the rigidity is by far the greatest in the direction ofthe corrugations while the rigidity of the board in the transversedirection is considerably reduced.

The invention seeks to provide a form of plastics material board orsheet material improved in the above respect.

According to the present invention there is provided a method ofproducing a corrugated sheet material which comprises supplying a filmof thermoplastic material in softened form to an embossing roller,embossing a series of interconnected corrugations onto the film andlaminating to the film so embossed to one or more further films so as toproduce the corrugated sheet material.

The invention further comprises a corrugated sheet material so made.

The corrugations produced by the embossing roller are "interconnected"by which is meant that all corrugations should not run parallel to oneanother as with conventional corrugated sheet materials, but that thecorrugations run in at least two, and preferably more, directions,thereby intersecting one another. A preferred form of corrugation is inthe form of interconnected star shapes as will be described more fullyhereinafter. The use of interconnected corrugations leads to severaldistinct advantages in the method and construction of the invention.Firstly, the rigidity of the sheet in all directions is improved.Secondly, the fact that the corrugations are interconnected leads toareas where air is entrapped and this also enhances the rigidity andimpact resistance of the sheet material.

The invention will be described further, by way of example, withreference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic plan view of a sheet material in accordancewith the invention;

FIG. 2 is a sectional view on line II--II in FIG. 1; and

FIG. 3 is a diagrammatic illustration of the method of production of thesheet material.

Referring to the drawings, FIGS. 1 and 2 illustrate a corrugated sheetmaterial generally designated 10 in accordance with the invention. Thiscomprises an upper film 12, a lower film 14 and a corrugated film 16therebetween. The film 16 comprises four series of corrugations whichinterconnect with one another in a regular manner producing a series ofstar shaped "cells". Two such cells are illustrated in FIG. 1 but itwill be appreciated that the entire sheet has many such cells in arepeating pattern. Assuming arrow A in FIG. 1 to be the direction ofproduction of the sheet, then corrugations 18 are in the direction ofproduction, corrugations 20 are transverse to the direction ofproduction, corrugations 22 are approximately 45° to the right of theproduction direction and corrugations 24 are approximately 45° to theleft of the production direction.

The sheet 10 may be produced by the apparatus illustrated in FIG. 3. Inthis, a first film 26 is fed from an extruder 28 into the nip of anembossing roller 30 and a co-operating chill roller 32. The surface 34of the roller 30 is embossed with a pattern corresponding to the starshaped cells of corrugations 18, 20, 22, and 24. It is preferred thatthe corrugations stand proud of the roller surface, but the oppositeconfiguration, with areas forming the corrugations recessed, may beemployed. The surface 34 of the roller 30 is also perforated and theroller is adapted to be connected to a source of vacuum so as to ensurethat the film 26 is pulled fully into the interstices of the embossedsurface 34. The roller 32 not only aids the film taking up the shape ofthe embossed surface 34 but, by its chilling action, stabilises the filmso that the embossed shape is retained as it leaves the surface 34 ofthe roller 30.

Before the latter occurs, a second film 36 also provided in a softenedform from an extruder 38 is applied to the outer surface of the film 26,now embossed. The film 36 adheres to the surface of the embossed film 26and forms the bottom of the eventual sheet material 10. If desired, andas illustrated in FIG. 3, a further film 40 supplied by an extruder 42is applied to the other surface of the embossed film 26 to produce thecomplete film as illustrated in FIGS. 1 and 2. Rollers 44 and 46 may bechill rollers in order to stabilise the applied film after it hasadhered it to the embossed film 26 so that the finally produced sheetmaterial 10 is stable and will not deform.

As can be seen from FIG. 1, the interconnecting corrugations 18, 20, 22,24 lead to a number of completely enclosed zones within which air istrapped. This adds to the rigidity and stability of the sheet as awhole. Moreover the fact that the various series of corrugations are atangles to one another ensures that effectively the sheet is rigid in alldirections approximately equally in contrast to the form of corrugatedsheet in which the corrugations are all parallel.

The sheet of the invention may be produced from any suitable plasticsmaterial but is particularly preferred to be produced from plasticsmaterial such as ABS, polystyrene, or especially polyolefins. Re-cycledmaterial may be used. However, where the end product is for the use inthe transportation or storage of food, it is preferred that at least thefilm 36 or 40, which will be in contact with the food, be produced fromvirgin material to avoid the possibility of contamination. However thesheet 26, and possibly the other of the sheets 36 or 40, may be producedfrom re-cycled material even when the sheet 10 is for use in foodtransportation packaging.

I claim:
 1. A method of producing corrugated sheet materialcomprising:softening a film of thermoplastic material, supplying thesoftened film to an embossing roller, embossing a first set of parallelcorrugations into the film, embossing a second set of parallelcorrugations into the film in transverse relationship to the first setof parallel corrugations, and laminating the film to a first outer filmof thermoplastic material by softening the first outer film and adheringthe films together at the outer extremities of the corrugations.
 2. Amethod as set forth in claim 1 further characterized by embossing athird set of parallel corrugations into the film in transverserelationship to each of the first and second sets of corrugationsrespectively.
 3. A method as set forth in claim 2 further characterizedby forming the second set of corrugations 45° from the first set ofcorrugations and forming a third set of corrugations 45° from each ofthe first and second sets of corrugations respectively.
 4. A method asset forth in claim 3 further characterized by laminating a second outerfilm of thermoplastic material to the opposite outer extremities of thefirst set and second set of corrugations to sandwich the corrugated filmbetween the first and second outer films.
 5. A method as set forth inclaim 3 further characterized by forming the first, second and thirdsets of corrugations to cross one another at a plurality of spacedcenters.